Transient process and optimal design of receiver coil for small‐loop transient electromagnetics

Distributed parameters of the receiver coils greatly affect transient electromagnetic signals over short time periods, causing a delay in the signal's effective sampling time and the loss of shallow exploration information. This paper investigates the influence of transient process on apparent resistivity calculation and analyses the relations between the error of apparent resistivity and receiver coil design. We find that, under the same effective area, different radii of the receiver coils lead to different levels of impact on the estimation of the apparent resistivity. An optimization model is proposed to determine the optimal receiver coil size that gives rise to the smallest estimation error of the apparent resistivity. The relationship between the optimal radius and the effective areas is developed, which serves as a guideline for the optimal receiver coil design. The results may provide a useful means for improving the accuracy of the small loop transient electromagnetic instrumentation for shallow‐depth mapping.

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